By Yesim Dikmen and Daren Butler ISTANBUL (Reuters) -Russian billionaire Roman Abramovich, who is sanctioned by the West over Moscow’s invasion of Ukraine, made a surprise appearance in Istanbul on Tuesday at the first direct peace talks in weeks between Russian and Ukrainian negotiators. The two teams sat facing each other at a long table in the presidential office on an Ottoman palace grounds. The Russian oligarch sat in the front row of observers wearing a blue suit, a Turkish presidential video showed. In the most tangible sign yet of progress towards ending the war, Russia emerged from th…